[OG10] Backporting + merge of GCC 10 into branch

[Tobias Burnus]

OG10 = devel/omp/gcc-10

e0e1d281472 Fortran: OpenMP - fix simd with (last)private (PR97061)
13ae89bc9c9 Merge remote-tracking branch 'origin/releases/gcc-10' into devel/omp/gcc-10
5a7ae4f073f [OpenMP] Fix mapping of artificial variables (PR94874)
3a6cb32b2c7 OpenMP/Fortran: Permit impure ELEMENTAL in omp directives
2dcc1721877 libgomp/target.c: Silence -Wuninitialized warning
76e74f04063 Merge remote-tracking branch 'origin/releases/gcc-10' into devel/omp/gcc-10

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